Electrodynamic sound reproducing apparatus



' Feb 25, 19%.

D. T. HINCHEN I 31,775

ELECTRODYNAMIC S'OUND REPRODUCING APPARATUS Filed April 28, 1934 Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE ELECTRODYNAMIC SOUND REPRODUCING APPARATUS Arizona Application April 28, 1934, Serial No. 722,933

5 Claims.

The present invention relates to an electrodynamic sound reproducing apparatus having an actuating coil which is held in a magnetic air gap by a transversely extending flexible centering member, and particularly to an arrangement for securing such a flexible centering member to a cooperating stationary abutment with a screw threaded means without subjecting the flexible centering member to a torsional strain during the assembly operation.

An object of the invention is to provide an improved arrangement for securing the fixed portion ofa flexible coil centering member, of an electrodynamic sound reprducing device, to a stationary abutment without subjecting it to a torsional strain.

At the present time, it is the practice to secure and center the actuating coil in the air gap of a magnetic field structure, of an electrodynamic sound reproducing device, by means of a transversely disposed flexible member which extends between the actuating coil and a stationary abutment adjacent the air gap.

In its preferred form; this flexible member has two circumferentially spaced relatively movable portions which are connected together by means of integrally formed non-radially or spirally disposed flexible arms, the whole unit being cut or punched, as one piece, from a flat sheet of fibre or like material.

It is now the practice, when such a flexible member is used, to glue one portion thereof to the diaphragm actuating coil and to secure the other portion to a stationary abutment by means of a machine screw. The use of a machine screw, in this manner, provides a simple, advantageous and effective means for securing the flexible centering member to the stationary abutment. This arrangement has the further advantage that the screw may be loosened at any time to permit a readjustment of the flexible centering member,

upon the abutment, to more accurately center the diaphragm actuating coil in the air gap. A disadvantage, however, in the use of a machine screw for this purpose is that the head of the screw has a tendency, when it is tightened upon the abutment, to twist or turn the portion of the flexible centering member engaged thereby. This produces torsional strain in the centering member and distorts the flexible arms thereof so that they can not function properly to maintain the coil centrally in the air gap and at the same time permit a truly axial movement of the coil when in operation. Therefore, unless time and special care is taken in tightening the machine screw, the

function of the flexible centering member may be entirely destroyed. In an extreme case it has been found that the distortion of the centering member, in this manner, has been sufiicient to actually break one or more of the flexible arms. When this occurs, the whole diaphragm and coil assembly becomes a total loss. The use of a simple washer beneath the screw head has been resorted to as a solution of this difliculty but, even with this expedient, time consuming care must be taken to avoid a turning of the washer and a consequent distortion of the flexible centering member.

In order to overcome the above difficulty and secure the flexible member upon a fixed or stationary abutment, in a speedy manner and without danger of distorting the same, the present inven-'- tion provides a means which will cooperate with the screw and the abutment to prevent a twisting or distorting of the flexible member when the screw is tightened upon the flexible member.

For a better understanding of the invention, reference should be had to the accompanying drawing wherein there is shown, by way of illustration and not of limitation, preferred embodiments thereof.

In the drawing;

Figure l'is a vertical sectional view of an electrodynamic sound reproducing device with its coil centering means secured in accordance with one embodiment of the invention,

Figure 2 is a fragmentary enlarged front view of the coil centering means, illustrated in Figure 1, with the securing means removed,

Figure 3 is an enlarged fragmentary sectional view showing a modified form of the invention,

and

Figure 4 is a perspective view of a part taken from the arrangement illustrated in Figure 3.

Referring to Figure 1 of the drawing, l designates a field frame having an energizing coil ll associated therewith. Disposed centrally within the field frame I0 and the energizing coil l I,

- there is an inner pole piece l2 which cooperates with an annular pole piece l3, at one end thereof, to form a magnetic air gap M. The annular pole piece I3 is shown as having a centering device l5-which serves to maintain the inner pole piece l2 centrally within the annular pole piece l3. The centering device [5 is constructed of non-magnetic material, such as brass or the like, and is cupped inwardly so as to provide a clearance adjacent the air gap l4 and also hold the energizing coil ll against axial displacement within the field frame In. Projecting outwardly from the field frame III, there is a diaphragm supporting frame I6 having a diaphragm II mounted thereupon. The diaphragm II is attached to its supporting frame I6 by means of a flange at its outer periphery which will permit an axial movement thereof. At the small end of the diaphragm I! there is an actuating coil -I8 which is disposed within the air gap I4 provided between the inner pole piece I2 and the annular pole piece I3. As a means for supporting and centering the actuating coil I8, within the -air gap I4, and at the same time permitting a limited axial movement thereof, the diaphragm I1 is provided with a flexible coil centering member I9 which extends transversely to the axis of the actuating coil I8 and over a stationary abutment 20 formed upon the end of the inner pole piece I2.

As shown in Figure 2 of the drawing, the flexible coil entering member I9 has an outer annular portion 2| and an inner annular portion 22, between which there is provided a plurality of spirally disposed flexible arms'23. When the flexible coil centering member I9 is of the socalled inside type, as illustrated in Figure 2 0f the drawing, its outer annular portion 2I .is generally glued to the diaphragm and coil assem-- bly at the point Where the actuating coil I8 is attached to the diaphragm I1 and its inner annular portion 22 is secured upon the stationary abutment 20 located centrally upon the inner pole piece I 2. In order to permit a limited transverse adjustment of the flexible coil centering member I9 upon the stationary abutment 20,.for the'purpose of properly centering the actuating coil I8 in the air gap I4, the hole through the inner annular portion 22 is made slightly larger than the securing means which passes "therethrough. At the present time, it is the practice to secure the inner annular portion 22, of the coil centering member I9, to the stationary abut ment 20 by means of a machine screw. However, when a machine screw is used in this manner, great care must be taken to prevent a distortion of the flexible coil centering member I9 by reason of the head of the machine screw gripping and turning the inner annular portion 22 as the screw is tightened into its final position. There is no practical way of holding the inner annular portion 22 stationary during this operation and, therefore, considerable time is consumed in effecting this final adjustment of the actuating coil II! in the air gap I4. As a substitute for the machine screw, for securing the flexible coil centering member I9 to the stationary abutment .20, the present invention contemplates, as shown in Figure 1 of the drawing, a bolt 24 having a nut 25 upon the end thereof. The bolt 24 has a rounded head 26, and a squared portion 21, somewhat similar to that provided upon a wagon bolt, immediately thereunder. The squaredportion 21 of the bolt 24 is dimensioned so as to flt snugly into a squared recess 28 formed within the stationary abutment 20. ment, the bolt 24 is held against turning when the nut 25 is tightened upon the end of the 'bolt 24, and as a result the head 26 can be drawn tightly against the inner annular portion 22, or the flexible coil centering member I9, so as to clamp it upon the stationary abutment 20, without danger of imparting any torsional strain or in any way distorting the flexible coil centering member I9. From this it will be seen that no precaution need be taken to avoid a twisting of With this arrangethe flexible coil centering member I9, and consequently the final securing of the actuating coil I8 in the air gap I4 can be carried out expeditiously and without the possibility of destroying the flexible coil centering member I9.

A variation of the above arrangement is that the squared portion 21 of the bolt 24 may be provided with an internal screw thread with which a long screw, not illustrated, that extends "from the rear of the speaker through the inner pole piece I2, will cooperate.

Referring now to Figures 3 and 4 of the drawing, wherein there is shown a modified form of thepresent invention, the numeral 29 designates an inner .pole piece having the stationary abutment 2|) withits squared recess 28 formed upon the end thereof. In this embodiment, instead of a hole-extending therethrough, the inner pole ,piece29 has a small threaded hole 30 at the bottom of the squared recess 28, into which a machine screw 3| maybe'tumed. Cooperating with the machine screw'3I, there is a clamping-member 32-havinga squared portion 33 which isadapted to'enter'the squared recess 28 in the stationary abutment 20, and an enlarged head portion 34 whichis adapted 'to overlie the inner annular portion-22 of the flexible coil centering member I9. =Whenthe' parts are assembled, as illustrated, themachine'screw 3| can be firmly tightened against the clamping member '32 to secure the flexible .coil centering member I9 upon the stationary abutment 20, without any danger of twisting or distorting the flexible coil centering member I9.

The invention has been illustrated and described in connection with a flexible coil centering member of theso-called inside type. However, it 'is to be'understood that the invention is also applicable :to :a flexible coil centering member of these-called outside type. foutside flexible coil centering member the inner portion thereof will be glued to the diaphragm and its annular or otherwise disposed outer portion -will=besecured upon one or more stationary abutments located externally of the diaphragm and'coil :assembly. The invention will be found particularly advantageous in connection with a -so-ca1led outside flexible coil centering member of the type .having a plurality of independently projecting spiral or non-radial arms.

1 While .I have, for the sake of clearness and in order to disclose my invention so that it can be readily understood, described and illustrated specific devices and arrangements, it is to be understood that this invention is not limited to the specific means disclosed, but may be em- .bodied inother Ways that will suggest themselves .to persons skilled in the art. It is believed that In the caseof an this invention is new and it is desired to claim it so :that all such changes as come within the Y scope of the appended claims are to be considered .as-part of this invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is 1. In a sound reproducing device of the character described, the combination of a pair of magnetic pole pieces disposed in spaced relation to form an annular air gap therebetween, an axially movable diaphragm coil disposed in said annular air gap, a stationary abutment disposed centrally of said annular air gap having a spline forming recess in the end thereof, a flexible centering member secured at its periphery to said diaphragm coil and disposed over said stationary abutment, a screw threaded member passing through said flexible centering member for securing said latter member upon said stationary abutment, and. means interposed between said screw threaded member and said flexible centering member having a portion extending through said flexible centering member and into the spline forming recess upon said abutment to prevent the turning of said flexible centering member when said screw threaded member is tightened against said abutment.

2. In a sound reproducing device of the character described, the combination of a magnetic pole piece having a bolt hole extending axially therethrough, an axially movable diaphragm coil disposed about the end of said pole piece, an extension upon the end of said pole piece having a squared recess in the end thereof and forming a part of said bolt hole, a transversely extending flexible member secured to the end of said diaphragm coil and disposed over said extension for centering said diaphragm coil about said pole piece, a bolt extending through the hole in said pole piece for securing said flexible member against said extension, and a threaded nut upon the end of said bolt, said bolt having a'squared portion disposed in the squared recess in said extension for preventing a turning of the bolt when the head thereof is tightened against said flexible member by a tightening of said nut upon the bolt.

3. In a sound reproducing device of the character described, the combination of a magnetic pole piece, an axially movable diaphragm coil disposed about the end of said pole piece, an extension upon the end of said pole piece having a spline connection forming recess in the end thereof, a transversely extending flexible coil centering member secured to the end of said diaphragm coil and disposed over said extension, a screw threaded member projecting through said spline connection forming recess and into the end of said pole piece for securing said flexible coil centering member against said extension, and

means carried. by said screw threaded member engaging said flexible coil centering member having a spline forming projection extending through said centering member and cooperating with the recess in the end of said extension for preventing a turning of said flexible coil centering member when said screw threaded member is tightened.

4. In a sound reproducing device of the character described, the combination of a magnetic pole piece, an axially movable diaphragm coil disposed about the end of said pole piece, a transversely extending flexible coil centering member secured to the end of said diaphragm coil and disposed over the end of said pole piece, a screw threaded member projecting through said flexible coil centering member and into the end of said pole piece, and means carried by said screw threaded member passing through said flexible coil centering member and engaging said pole piece for securing said flexible coil centering member in a fixed position upon the end of said pole piece and preventing a turning thereof when said screw threaded member is tightened upon said pole piece.

5. In a securing means for an inside type of centering spider for an electrodynamic cone diaphragm, the combination of a center pole piece having an abutment formed upon the projecting end thereof, a diaphragm having an annular actuating coil disposed about said pole piece, a flexible transversely extending coil centering member secured to said diaphragm and at one DONALD THOMAS HINCHEN. 

